| In recent years, the rapid development of aviation and automobile industry and the rising requirements on energy conservation and environmental protection lead to an increasing demand on high-grade lubricant oil. As a result, synthetic PAO lubricant oil attains extensively applications in above several fields owing to its excellent properties. The lacking of technology for producing alpha olefins and synthesizing poly-alpha-olefins (PAO) in China has been resulting in a dependence on imported high-grade PAO synthetic oil for many years. Such a study on novel technology for preparing high-quality PAO lubricant oil using alpha olefins is therefore very important and of great significance in order to change the adverse situation of dependence on imported high-grade PAO synthetic oil. In this study, the immobilized catalysts used for polymerization of alpha olefin were prepared by applying different methods, the activity and stability of the catalysts were investigated in a fixed-bed reactor. In addition, the mechanisms for deactivation of immobilized catalyst were analyzed and the pseudo slurry bed oligomerization process was investigated.Firstly, AICl3and TiCl4were used as active components while activated carbon, γ-Al2O3, and molecular sieves were used as supporters. The immobilized catalysts were prepared by using impregnation and gas phase loading methods. The immobilized catalysts were evaluated in a fixed-bed reactor, using1-decene as raw material. The results show that coal-based activated carbon and γ-Al2O3are better carriers for preparing immobilized catalyst by using impregnation method. These two immobilized catalysts show high yields of PAO, nearly90%, in initial period and around50%yields after16h time-on-stream. Furthermore, the stability of AlCl3-TiCl4/γ-Al2O3catalyst can be improved by using gas phase loading preparation method. The yield of PAO is found93.63%in initial period and maintains50%after50h time-on-stream. The properties of product are highly stable, v100(kinematic viscosity of100℃) is about10mm2/s, VI (viscosity index) is higher than140, and FP (freezing point) is lower than-65℃.Then, the effects of raw monomers, reaction temperature and space velocity on oligomerization were researched by using AlCl3-TiCl4/γ-Al2O3catalyst prepared by gas phase loading method, and the oligomers were analyzed and characterized. The optimized oligomerization conditions are found as:reaction temperature80℃, LHSV0.5h-1. Under these conditions, the yields of PAO synthesized using1-octene,1-decene, and1-dodecene are all greater than90%in the initial period. After hydrogenation, v100, V40(kinematic viscosity of40℃), VI, FP and flashing point of PAO are10.22mm2/s,61.36mm2/s,154,-58℃, and248℃, respectively. The main properties meet the requirements of commercial PAO-10product. H NMR, C NMR, and GPC analyses show the branched degree, the end methyl content, and the dispersion index are0.1867,0.1527, and1.38, respectively.Furthermore, the deactivation mechanism for immobilized catalyst were analyzed and discussed by combining chloride content test with BET and TG-DSC analyses. The results show that the loss of active components is the main reason for the deactivation. Meanwhile, some oligomers adsorbed in catalyst internal surface, cause pore blocking effect thus, decrease oligomerization performance and catalyst life to some extent.At last, the pseudo slurry bed oligomerization process was investigated. The yield of PAO is found over60%after150h time-on-stream with the conditions of reaction temperature80℃and LHSV0.5h-1. The main properties of synthesized product meet the requirements of commercial PAO-15lubricant base oil. In comparison with fixed-bed process, the pseudo slurry process has more than one time larger producing time and almost20percentages higher yields of PAO. |
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